Electfic tach was standard for america for the C. You are referring to the electric tach oil pump cover which also had a different drive gear used.
European cars had the european heater boxes which were the precursors of the 911 heater boxes. There was a clip on the rear left heater box to hold the tach cable. All the heads of the european heater cars had black anodised heads like the s-90 engines.

I may be old, and my memory is sometimes a little fuzzy, but I've been driving and working on 356s since 1964, and I don't recall Cs or SCs as having electric tachs as standard equipment. That said, I could be wrong. PET for USA cars seems clear to me ...

The Cap'n

If it matters now, Cap'n and Matt refer to my post. Both of you have some wrong impressions about this.